Typically, a blind transport system will have a head rail which both supports the covering and hides the mechanisms used to extend and retract or open and close the covering. Similar systems are used for horizontal blinds and for vertical blinds. One such blind system is described in U.S. Pat. No. 6,536,503, Modular Transport System for Coverings for Architectural Openings, which is hereby incorporated herein by reference. In the typical top/down horizontal product, the raising and lowering of the covering is done by a lift cord or lift cords suspended from the head rail and attached to the bottom rail (also referred to as the moving rail or bottom slat). The opening and closing of the covering is typically accomplished with ladder tapes (and/or tilt cables) which run along the front and back of the stack of slats. The lift cords usually run along the front and back of the stack of slats or through holes in the slats. In these types of coverings, the force required to raise the covering is at a minimum when it is fully lowered (fully extended), since the weight of the slats is supported by the ladder tape so that only the bottom rail is being raised at the onset. As the covering is raised further, the slats stack up onto the bottom rail, transferring the weight of the slats from the ladder tape to the lift cords, so progressively greater lifting force is required to raise the covering as it approaches the fully raised (fully retracted) position.
Some window covering products are built in the reverse (bottom up), where the moving rail, instead of being at the bottom of the window covering bundle, is at the top of the window covering bundle, between the bundle and the head rail, such that the bundle is normally accumulated at the bottom of the window when the covering is retracted and the moving rail is at the top of the window covering, next to the head rail, when the covering is extended. There are also composite products which are able to do both, to go top down and/or bottom up.
In horizontal window covering products, there is an external force of gravity against which the operator is acting to move the expandable material from one of its expanded and retracted positions to the other.
In contrast to a blind, in a top down shade, such as a shear horizontal window shade, the entire light blocking material typically wraps around a rotator rail as the shade is raised. Therefore, the weight of the shade is transferred to the rotator rail as the shade is raised, and the force required to raise the shade is thus progressively lower as the shade (the light blocking element) approaches the fully raised (fully open) position. Of course, there are also bottom up shades and composite shades which are able to do both, to go top down and/or bottom up. In the case of a bottom/up shade, the weight of the shade is transferred to the rotator rail as the shade is lowered, mimicking the weight operating pattern of a top/down blind.
In the case of vertically-oriented window coverings, which move from side to side rather than up and down, a first cord is usually used to pull the covering to the retracted position and then a second cord (or second end of the first cord in the case of a cord loop) is used to pull the covering to the extended position. In this case, the operator is not acting against gravity. However, these window coverings may also be arranged to have another outside force or load other than gravity, such as a spring, against which the operator would act to move the expandable material from one position to another.
A wide variety of drive mechanisms is known for extending and retracting coverings—moving the coverings vertically or horizontally or tilting slats. A number of these drive mechanisms may use a spring motor to provide the catalyst force (and/or to supplement the operator supplied catalyst force) to move the coverings.